Quinine sulfate dihydrate is primarily used as an antimalarial medication to treat and prevent malaria, particularly in regions where the disease is resistant to other treatments like chloroquine. It works by interfering with the growth of parasites in red blood cells. Additionally, it is prescribed for nocturnal leg cramps due to its muscle relaxant properties and utilized in small doses as a flavoring agent in beverages for its bitter taste. In laboratory settings, it serves as a high-purity biological reagent (99.0%) dedicated for fluorescence analysis, exhibiting excitation at 347 nm and emission at 448 nm in 0.5 M sulfuric acid. Its use is regulated due to potential side effects such as cinchonism, including tinnitus, headache, and nausea. It is also employed in medical research to study cardiac and neurological functions.